1. Field of the Invention
The present invention relates to an optical communication apparatus.
2. Description of the Related Art
FIG. 8 is a block diagram for explaining an example of the constitution of a conventional optical communication apparatus. There is a diode (hereinafter, abbreviated as LD) 1 which converts an electric signal into laser beam having a corresponding intensity and transmits the laser beam to outside via an optical fiber, not illustrated. An LD driving unit 2 drives LD 1 in accordance with transmission data (Tx. Data) inputted via a signal line 3 and an output signal 7 from APC (Auto Power Control) 5. A portion of the laser beam emitted from LD 1 is incident on a photodiode 4 and the photodiode 4 converts the incident laser beam into an electric signal.
APC 5 controls the LD driving unit 2 in accordance with the electric signal outputted from the photodiode 4 and a reference amplitude (Tx. Ref) of a transmission signal inputted from a signal line 6 such that the intensity of the laser beam emitted from LD 1 becomes a predetermined amplitude. Laser beam transmitted via an optical fiber, not illustrated, is incident on a photodiode 8 and the photodiode 8 converts the laser beam into a corresponding electric signal. An amplifying unit 9 amplifies the electric signal outputted from the photodiode 8 by a predetermined gain and outputs the electric signal to an inner portion of the optical communication apparatus as reception data (Rx. Data) via a signal line 10.
The transmission data is supplied to the LD driving unit 2 via the signal line 3. The LD driving unit 2 drives LD 1 to emit laser beam in accordance with the transmission data and the output signal 7 from APC 5. The laser beam emitted from LD 1 is transmitted to other party of communication, not illustrated, via an optical fiber, not illustrated.
The portion of the laser beam emitted from LD 1 is incident on the photodiode 4 and accordingly, an electric signal in correspondence with the intensity of the laser beam emitted from LD 1 is inputted to APC 5. APC 5 compares the electric signal outputted from the photodiode 4 with the reference amplitude (Tx. Ref) of the transmission signal inputted from the signal line 6 and controls the LD driving unit 2 such that both maintain a predetermined relationship (for example, such that both are equal to each other). As a result, the intensity of the laser beam emitted from LD 1 always becomes a predetermined amplitude.
Further, the laser beam transmitted via an optical fiber, not illustrated, is photoelectrically converted into the corresponding electric signal by the photodiode 8, amplified by the amplifying unit 9 by a predetermined gain and thereafter is outputted to the inner portion of the optical communication apparatus as reception data via the signal line 10.
According to the above-described conventional optical communication apparatus, the intensity of the transmitted laser beam is always set to be a predetermined amplitude. It is general that the intensity of the laser beam is set with transmission loss of a longest optical fiber as a reference in a system thereof (a system constituted by connecting optical communication apparatus to each other).
When a power value of laser beam is set to an intensity capable of sufficiently dealing with transmission loss in an optical fiber having a longest length in a system, the system can ensure a sufficient intensity (power value).
It is said that the life of a laser diode (LD) is inversely proportional to the second through the third power of an intensity of emitted laser beam. Therefore, in the case in which an intensity of laser beam which can communicate through an optical fiber having a longest length which is predicted in using the optical fiber in a system when communication is carried out by an optical fiber having a short length, the intensity becomes excessively heavy and the life of LD is significantly shortened.
That is, in the case in which the intensity of laser beam which can communicate through the optical fiber having the long length which is predicted in using the optical fiber in a system, when lengths of optical fibers used differ from each other significantly, the intensity of laser beam inputted to a reception unit of an optical communication apparatus similarly differs significantly. For example, in the case of LAN (Local Area Network) or the like, the length of an optical fiber used is varied significantly substantially from 1 m through 2 km and accordingly, a difference in transmission losses becomes about 16 dB and the intensity of laser beam is varied significantly in accordance therewith. Such a difference is particularly significant in POF (Plastic Optical Fiber) having large transmission loss.
When the intensity of inputted laser beam differs significantly in this manner, in order to ensure an error rate at a constant value or lower in respect of input of laser beam in any intensity, the dynamic range of light in an optical communication apparatus needs to provide sufficiently widely, as a result, there poses a problem in which design of the apparatus becomes complicated and fabrication cost of the apparatus is increased.
Further, when the problem of Eye Safe is considered, it is preferable to set the intensity of laser beam as small as possible. When the intensity of laser beam is set low, in a system having significant loss (for example, a system connected by POF or the like), there poses also a problem in which the design becomes difficult owing to the problem of the dynamic range as mentioned above.
A conventional optical communication apparatus is not constituted such that control of light emitting power and reception sensitivity is dynamically carried out in accordance with a kind, a length, a situation of laying thereof, a condition of using thereof or the like of an optical fiber used. Therefore, the optical communication apparatus including the optical fiber needs to fabricate under a severe specification conscious of the worst condition, as a result, the apparatus becomes expensive. This is significant particularly in the case of using an optical transmission medium having comparatively large transmission loss such as an optical fiber made of plastic.
Therefore, the present invention relates to an optical communication apparatus resolving the above-described problem and capable of firmly executing optical communication using an optical transmission medium among optical communication apparatus under an optimum condition.
Hence, according to a first aspect of the present invention, there is provided an optical communication apparatus connected to an optical communication apparatus on other party side via an optical transmission medium for communicating a data signal with the optical communication apparatus on the other party side, the optical communication apparatus comprising drive signal outputting means for controlling a signal level of an input signal in accordance with a light emitting power control signal and outputting the input signal the signal level of which has been controlled as a drive signal, a light emitting element for emitting light at an intensity in accordance with the signal level of the drive signal and transmitting an optical signal via the optical transmission medium, test signal generating means for forming a test signal having a specific signal pattern, selecting means for selectively outputting either of the test signal and the data signal to the drive signal forming means as the input signal, a light receiving element for receiving the optical signal via the optical transmission medium and converting the received optical signal into an electric signal, detecting means for detecting whether the electric signal outputted from the light receiving element coincides with the specific signal pattern when the selecting means selects the test signal and controlling means for controlling a parameter of the light emitting power control signal based on a result of detection by the detecting means, wherein when the detecting means detects that the electric signal does not coincide with the specific signal pattern, the controlling means controls the parameter of the light emitting power control signal such that an intensity of the optical signal outputted by the light emitting element is increased and when the detecting means detects that the electric signal coincides with the specific signal pattern, the controlling means sets a current value of the parameter of the light emitting power control signal as the parameter when the selecting means selects the data signal.
According to the first aspect of the invention, when the detecting means detects that the electric signal does not coincide with the specific signal pattern, the controlling means controls the parameter of the light emitting power control signal such that the intensity of the optical signal outputted by the light emitting element is increased and when the detecting means detects that the detected signal coincides with the specific signal pattern, the controlling means sets the current value of the parameter of the light emitting power control signal as the parameter when the selecting means selects the data signal. Thereby, the intensity of the optical signal is sets to be small initially. When the intensity of the optical signal is increased by controlling the parameter of the light emitting power control signal and the coincidence of the result of detection is established, the controlling means sets the parameter of the light emitting power control signal as the parameter when the selecting means selects the data signal. Accordingly, optical communication among the optical communication apparatus is firmly carried out by reducing transmission loss in optical transmission under an optimum condition in accordance with the length of the optical transmission media.
According to a second aspect of the invention, there is provided the optical communication apparatus according to the first aspect wherein the specific signal pattern of the test signal formed by the test signal generating means is previously set to be different from a signal pattern of a test signal outputted from the optical communication apparatus on the other party side, the selecting means comprises a first selector for selectively outputting either of the test signal formed by the test signal generating means and the electric signal outputted from the light receiving element, and a second selector for selectively outputting either of an output from the first selector and the data signal, wherein the controlling means controls the selecting means such that when the test signal having the signal pattern different from the specific signal pattern is detected, the first selector outputs the electric signal and the second selector outputs the electric signal which is the output from the first selector.
According to the second aspect of the invention, in the operation of the controlling means, when the test signal having the signal pattern different from the specific signal pattern is detected, the first selector can output the electric signal and the second selector can output the electric signal which is the output from the first selector.
According to a third aspect of the invention, there is provided the optical communication apparatus according to the first aspect, further comprising an intensity detecting light receiving element for detecting the intensity of the optical signal transmitted from the light emitting element, wherein the controlling means stops controlling the parameter which is carried out when the detecting means detects that the electric signal does not coincide with the specific signal pattern in a case in which the intensity of the optical signal detected by the intensity detecting light receiving element becomes a limit value or more.
According to the third aspect of the invention, in the operation of the controlling means, when the intensity of the optical signal detected by the intensity detecting light receiving element becomes equal to or more than the limit value, the operation can be stopped by stopping to control the parameter which is carried out when the detecting means detects the incoincidence and the optical communication can be prevented from being carried out at the intensity of the optical signal which is equal to or more than the limit value.
According to a fourth aspect of the invention, there is provided the optical communication apparatus according to the third aspect, further comprising storing means for storing the limit value of the light emitting element for emitting light, wherein the controlling means stop controlling the parameter when the intensity of the optical signal detected by the intensity detecting light receiving element is equal to the limit value.
According to the fourth aspect of the invention, the controlling means can stop controlling the parameter when the intensity of the optical signal detected by the intensity detecting light receiving element becomes equal to the limit value.
According to a fifth aspect of the invention, there is provided the optical communication apparatus according to the first aspect wherein the controlling means controls the selecting means such that the data signal is outputted after the parameter of the light emitting power control signal has been set.
According to a sixth aspect of the invention, there is provided the optical communication apparatus according to the first aspect, further comprising time measuring means for measuring a time period from a timing when the light emitting element transmits the test signal.
According the sixth aspect of the invention, there can be known the time period from the timing at which the test signal has been transmitted in accordance with the time period measured by the time measuring means.
According to a seventh aspect of the invention, there is provided the optical communication apparatus according to the sixth aspect, further comprising informing means for informing an abnormality to a user based on a signal indicating the abnormality outputted by the controlling means, wherein the informing means informs a user of the abnormality by outputting the signal indicating the abnormality when the controlling means has not set the parameter of the light emitting power control signal until the time measuring means has counted the predetermined time period from the timing when the light emitting element transmitted the test signal.
According to the seventh aspect of the invention, the informing means can inform a user of the abnormality by the signal indicating the abnormality.
According to an eighth aspect of the invention, there is provided the optical communication apparatus according to the first aspect, further comprising amplifying means connected between the light receiving element and the detecting means for amplifying the electric signal converted by the light receiving element based on a predetermined gain and outputting the amplified electric signal to the detecting means.
According to the eighth aspect of the invention, the amplified electric signal can firmly be provided to the. detecting means.
According to a ninth aspect of the invention, there is provided the optical communication apparatus according to the eighth aspect wherein the amplifying means comprises an analog/digital converting unit for analog/digital-converting the electric signal.
According to a tenth aspect of the invention, there is provided the optical communication apparatus according to the eighth aspect wherein the controlling means controls the gain based on the result of detection of the detecting means.
According to the tenth aspect of the invention, the gain in amplifying the electric signal of the light receiving element can be controlled optimally in accordance with the result of detection.
According to an eleventh aspect of the invention, there is provided the optical communication apparatus according to the first aspect wherein the test signal is a signal having a specific rule which is not provided to the data signal.
According to the eleventh aspect of the invention, the test signal can clearly be discriminated from the data signal.